Overclocking Guide

Special Precautions For 75 And 83 MHz Bus Speed

Using this higher bus speeds includes some important restrictions which you should be aware of.

• The PCI bus runs at 37.5 or even 41.6 MHz. This can lead to several problems with PCI devices. Typical trouble makers are SCSI controllers, some video cards, and network cards. SCSI controllers and network cards often refuse to work at the faster speed, but some video boards just get much hotter than usual. If you find a way to cool these video cards, you shouldn't have any trouble. My Diamond Stealth 64 Video VRAM isn't affected at all by those higher bus speeds. I hope the 75/83 MHz bus speed survey will help us find out which PCI devices run at higher PCI bus speeds.
• The speed of the EIDE interface included with the chipset is not only determined by the PIO or DMA modes, but is also highly dependent on the PCI clock. This is one reason why the EIDE interface is always slower in systems with 60 MHz bus speed or less. This is also valid in the other direction, meaning your interface will be faster when you are running at 75 or 83 MHz bus speeds than at 66 MHz. At first this sounds fine, but often either the interface or, in more cases, the hard disk isn't up to the faster bus speeds. My HDDs work fine at 75 MHz bus speed, but at 83 MHz I have to reduce the PIO down to 2. The same is valid for EIDE CD-ROM drives. This could be the cause if you are running into strange lock-ups in windows.
• The Asus P/I-P55T2P4 is one example of a board that does not allow you to adjust the ISA bus speed. It seems to be a fixed divider from the PCI clock. This can cause sound cards to run into trouble if they don't like the higher ISA bus speed. I haven't come across this problem myself yet, but I've heard of one fellow whose AWE 32 produced strange sounds when running at a faster speed. If you run into this, increase the ISA wait states in the BIOS setup to try to remedy the problem.
• Let me say again that the RAM type and quality is of great importance. Most 60ns EDO will run fine at 75 MHz bus speed, but for 83 MHz you'll need high-end EDO or SDRAM (as long as the motherboard supports it).